Method of and machine for making piston rings



Sept. 4, 1951 A. H. BATES 2,566,304

METHOD OF AND MACHINE FOR MAKING PISTON RINGS 2 Sheets-Sheet 1 Filed Oct. 15 1943 Sept. 4, 1951 A. H. BATES METHOD OF AND MACHINE FOR MAKING PISTON RINGS Filed Oct. 15. 19 45 2 Sheets-Sheet 2 x? M O \L w vim/ 1 Z w n\ w S 4 V b x 4 m m m\ fi ww l J 3 #1 w w N 7 7%///////// J 2-111-1 3 v .3 a s? N Q @N @w Q Q m \\\N\ Wm N Q u .3 mm, 3 \w MN Mm, on WW em 3 WT *N m mu on i raiaasd scribdabo afche. urni sa di cr n Patented Sept. 4, 1951 UNITED STAT-Es METHOD OF sitar f1 AnD-MAGHI'NECFOR MAKING .HSI NG Rockford-11L, assignor to Burd PistbnRiifgTCbmpany, Rockford, 111., a corpora- ,The-present invention relatesto a new and useulim im .fotm k n Piston i a-zan a m chine ,particularly suited to. turmthesevrings on theyquter periphery-and finish them (on the inner periphery, in sequence or at-the same time. 5

glngeneral, piston rings for automotive engines are cast :or formed; out: .of round, as disclosed by; many patents. The ring isside ground to produce true ilat, smooth, and parallel surfaces -on botiisid s Aggapis thentcut or formed, leavin sthe ring-Yin the form' of anopen resilient spring, illus trated in Fig. 1. -'I;he;rings are then stacked inrowssin various kinds of closing fixtures; which: clqse-th nuntil he r s-a e ox m t l circulan, They are then clamped endwise on an 'th suitable ycollars, all as disclosed by:

1 art; 'Ih e prings. arethen turnedor round alat e Similar device t amired outside flnish, smoothness, and-diameter. .Some times the. rinesza e. h.: lw1-. v descr ed and; hen;released fromthe elarnping; eollarsyand arbor, and again. closed :and clampeda, second time andfinished turned or ground =to;-produce a truer smoother, finish; on the v utside, diameters Aftergelease from the clampingdevice, the rings' ane generally againclosed andv placed, inside a sleeve or boringfixtureand clampedaxially while theyare rough and: finish bored. In other (Words;- the seqlience ofyturningand boring operations, described is, after .sid,e. grinding:

1: Close and clam'p'on arbor; 2; Rough turn I g 3.:Relje'asefrom arbor; if 4.-Cl o's--a'nd clamp on arbor; 5.- Finish turn; V

65 Release-from arbor '2 'Place in" closing device; B.- Roi1gh bore;and

9. 'Finish bore.

-l... .-4O Thissequence may be varied/to suit' requirements'; for instance, rough turn, rough bore, finish bore, finish turn;

.In these turning and boring soperationa it is apparentthat the labor of' handling closing and clamping fixtures and' putting' theufi'xtures into turning andbocring machinesis a. large part ofw theworkirequired to complete the turning and boringoperationsm lngaccordanceyvith thej, method. of. my .in vem ,160 tiQI-irrthfi: iturningyand; boring l-ofipiston rings; is edina shed,withoututheneed f r any-meoha'ni i ll operatedielos a d v c s;iarbo sacolla s being accomplished at the same time or in se- Anglicans clitoral-.15, 1943,1Serlal No. 506,342 15 claims. (01.29 27) quence inone operation. In other words, Within? new method, only'the rings areplaced in? the ma chine; They are closed, turned-bored andrer leased all within the machine and without "the necessity of their being handledeven oncein any intermediate stage of the process. :s: Theinvention is illustrated in the accompany-V ing drawings, in which: e Fig. 1 is a face view andv edge view of a-piston ring such as the machine of my invention is adapted to operate upon; i 'Fig. 2 is a side elevation of the machine of my invention; i-

m; Fig. 3 is a longitudinal sectionofi the main .por-, tions of the machine, on a largersca-le;

Figs, '4 to '7 are sections on the numbered lines of Fig; 3;? a Fig. 8. is a longitudinabsectlon of theispring' blade shown inFig. 6,,showing thewideningw'oi the end portion at the .point where the outside turning is commenced, and i ;Fig. 9 is a fragmentary sectional",viewjoorre sponding to a portion of Fig. 3 but showing a different relationship of the turning and boring tools for turning and boring at the same time,

instead of in sequence.

Similar reference numerals are applied to corresponding parts in these views.

,';Referring to Figs. 2 and 3, mainly, sthe refere ence numeral [0 designates a hydraulic-cylinder.

withpiston and'piston rod ll and-.pusher; l2. mounted on end of piston'rod; 'Thishydrauli'c' mechanism is actuated by a. commercial high pressure hydraulic pump and is regulated 'by coma mercial hydraulic controls to perform the follow-'- the'quick approach, followed by aicontriolled feed to any desired stroke; atltheend' ofthes'troke', the pusher trips '9. leveriandstlie pusherreturns automatically to its startingqpoint' and is ready for a new cycle, whena new load of rings is placed on adjustable guides l3. w

most universally in the machine-tool industryvy i4 is a hollow cylindrical casting'm'ounted n) This annular castingi has; a :hollow: bearing hub 16 throughout its length supported bracket l5.

solely by ribli. Notches l8 are-provided-to make space through the length, of the cylinderrl'l, for," the-adjustable guide bars I3; The, lattertrhavei" adjustingbrackets 19to permit radial-adjustment? of the guides relative to the cylinder M to suit correspond gly 4 3 difierent sizes of rings being operated upon. At its discharge end the cylinder [4 carries a main external chuck in the form of an annular tapered sizing ring 20. This ring is smoothly and accurately finished and highly polished, and its smallest inside diameter is sized closely to suit ring size being handled.

Sizing ring 2!) .carries a spring 2| or blade or doubleblade form, which when split rings are pushed through the cylinder [4 with their gaps slipping over the rib l1 and nearly closed,

after passing hollow conical taper 22 in the sizing ring 20, serves to generate a substantial expanding pressure on the adjacent ends of the ring at the gap. This expanding pressu-re makes the split ring conform closely to the bore of the sizing ring 20 and also prevents rotary motion of ring caused by the turning-bfiingdjone on, the outside. 23 is a retaining ring which keeps the sizing ring 20 in place, The cylinder l4 also carries on its periphery a driving head '24 that is given rotary motion: by any suitable driving means. I haveindicate'd a V-belt drive, but could use almost any controlled steady drive of required capacity and :R. P. M.

Head 24 carries aturning tool or tools 25, preferably a plural number, also a plural number of steady rests 26 that-bear on the periphery of the rings at eircumferentially spaced points, as shown in Fig; 5, to help keep the same central while-they are being- -turned and bored, while passing from the sizingiring 2ll-to the auxiliary external chuckin 'theiform' ofa sleeve 21. 21 is a hollow annular sleeve of an inside diameter at its ends to suit. a.:rough turned ring. Sleeve 21 is smaller in inside ,diameter. at its ends 21a and 21b than the sizing ring20, and has a blade or blades 28 throughout its;leng th....The-intermediate portion 2.1c.iof--.the bore of the sleeve 21 is enlarged so that there is. less frictional drag on the operation of..the.machine and still just as much ultimate accuracy. in. its production. The sleeve '21 is as closely placed axially to the sizing ring 20 as is possible ,toclear the turning tools 25 and steadyrests:26. For instance, when turning rings wide; the-space axially from 21 to 20 might be about ed by an annular or .hollow. cylindrical casting 29, which is very similar to'the cylinder [4 but which does not have hollow hub IE or rib I1. The. cylinder! 29 ;is supported .by aibracket 30, which may beidentical to. bracket IS. The head 3| revolves about the cylinder29 and may be identical to the head.24,..and bedriven likewise. The head 3| carries turningtocls 32 and also steady rests 26, which may beidentical with the tools 25 and steady rests 26, but these tools and rests are sharpenedand set for a finishing cut.

33 is an annular sleeveof a size internally suited to the outside'diameter of. finish turned ring and is locatedaxiallyaszclose to the sleeve 21 as possible, and carries a guide. blade 34 extending lengthwise of the inside thereof to fit slidably in the ring gaps and keep these gaps aligned with the guide 44. The blade 34 may be of either of the two types 2l and 28 if an expanding pressure is desired, but willotherwise be a fixed blade of approximately the widthof the web portion of the I-section guide-44. Sleeve 33 is demountably supported in a bracket 36, which, in turn, is anchored to the base 31.

The blade 28 is constructed, as shown in Fig. 7, to give an expanding or spreading pressure on the opposite ends of the ring at the gap, such expanding pressure being desirable where the The sleeve 21 is support-' sleeve 21 holds the rings while they are being bored by the boring tool or tools 35 and especially where the rings are turned and bored at the same time, as illustrated in Fig. 9. The short length blade 28 at the outgoing end of the sleeve 21 is similar to theblade 2|, shown in Fig. 6, and is preferably flared like that blade, as indicated in Fig. 8, a change-over from a blade of the externally projecting type 28 to the internally 19 projecting type 2| being necessary at the outgoing end of the sleeve 21 because of the fact that the rings are given their finish turning at that point by the tool or tools 32. I 38 is a. bearing bracket rotatably supporting a 5"drive shaft 39:2.11140 is a drive gear or other means for transmitting rotative force or torque through the shaft 39 to the boring head 4| and single or. multiple cutting tool 35. The inner end of shaft 39 is suitably supported in bearings 42 in the hub l6, so as to be in true concentricity with respect to the cylinder l4 and sizing ring 20. The operation of the machine-isas follows: Split rings are grouped in cylindrical stacks, say

six to twelve inches long,; and placed on adjust-- able guides I 3 in front of pusher l2 on piston" rod l I. Gaps in the rings are in line with rib I1. The operator trips a starting lever and pusher l2 advances giving a controlled feed. The first- I load of rings will advance into the cylinder I4 with ring gaps fitting over rib [1. The second or succeeding loads push first load into the sizing ring 20. As the rings advance through the small cylindrical portion 43 of the ring 20, they are presented to turning tools 25, and each tool 25 5 cuts a successively deeper out. As ring is turned, it is supported by steady rests 26 and advances into sleeve 21. When a ring has entered the sleeve 21, or is entering, boring tools in boring head 41 bore the inside and the'ring advances through sleeve 21 tothe other end of the sleeve;

a .r: where finish turning tools 32 finish turn the outside diameter. The ring at this point is supported again by steady rests,- like those at, and ad-'- Traveling through the 45 sleeve 33, the rings drop out of the far end, andvancesinto sleeve 33.

their gaps are slipped over and into an I-section guide 44, which delivers the ringswith their gaps properly presented at 45,'where the shaft 33 is reduced in diameter to less than the width 01' the ring gap for easy passage of the ring past the shaft. The ring is then guided along the lower I-section guide 46 throughthe base 31 of the machine to the outside of themachine, where it may be removed, the finishedrings collecting in a group on the substantially horizontal delivery end portion 41 of the guide 46, as indicated in Fig. 1. At the outset, the firstfew groups or rings fed through the machine will bedurnmy rings that are finished rings and, hence, are smaller in outside diameter and larger in inside diameter than the rough ring blanks to be machined. These dummy rings will pass through the sizing ring 28 and past the turning tools 25 and boring tools 35 without being machined thereby, and 5 will pass through the sleeve; 21, and from the sleeve 21 past the turning tools 32 into the sleeve 33 without being machined. Then, when the machine is filled with dummy rings clear to the outgoing end of the sleeve 3.3, .the first group of rough ring blanks to be machinedwill be I placed on the guides l3 in front of the pusher l2 for passage through the machine. In that way I -the rings to be machined are assured of proper support in the turning and boring operations,- the dummy rings aheadof the-rings being machined r and 28 on a larger scale.

ends of the machine to clear a ay the edits end dust quickly and thuskeep iriel'cfii'ne oper In Fig. 9, the tools 25', and as er dispo a weenie turning and borihg'op' ti e g ne at the same time instead 61' in soon j S disposition of the tools isefitii'ly prjac feel and reasibleiii operating on tni'ckerrines; wh ch case the ring is still in engagement h bl'afde 2| it threads" Ontd 2 g commences in case's heiof p Y completed. Where .borir'ig" and turning are done at the same" tiffie, the bciririg need will; e: tame iii the opposite direction relative" to the turning tool or tools 25, to balan'e the" oppsingftorque reactions on the rings due" t6 machi r li fig tfi outer and inner peripheries at the same tirii' v K The sections Figs. 6' and renew" the b a es 2| e er n w F 6, 48 is a Soft metal insert to which the erid 49 of one leg of the lei-shaped blade" rs suitably attached, as by grazing. The other l'jg'5ll is therefore free to move to the wrest?" fi'fifihth fixes leg, to exert spring ressure expand the R accurately to the inside" dial t'r c'ifjh sizing ring 211 The blade 21', as" s'hdw'nj'fi m 8', has the, legs substantially parallel throughout the major portion of the mute-merrier, lii ut alt'the outgoing end the legs are spread apart, as ifidi cated at 5|, to increase the expan ng press-ere just prior to and during the time that: the ring undergoes the turning operatiori,. at which time it is; of course, most important ra time standpoint of accuracy in' size thatthe rin 'ne' conformed most accurately" to the inside iameter of the sizing ring 20. The bore 43 of the-sizing ringlil is preferably a few thousandths of ani'ncli larger in diameter up to the outgoir'i g" end portion thereof, so that there will be less menenardrag on the operation of the inach'ihe" ems'till just as much accuracy in its production,-.only'tlieoiitgoing end portion of the bore 4' 3b"eiii 'fo'f thesi'ze Of ririg desired. In other words, the flhg is' ob'h tra'cte'd' slightly as it pass'e's'thi'oiighf the oiit end portion of the bore and at'th sarrietime the bla'de2'l exerts an increased e'i'r anam'gpressure, with a view toobtainingclosei'fa'cciiracy'in the turning operation; While I naye hbwnin Fig; 8 a single continuous" blad'e'fi 'of uniform expander width throughout the major portion T its length and flared for increasedfeiiparider ac tion at the outgoing end; it should; endorse-g be understood that I- may provide" a separate blade section of flared form to take the" filaceof' the end portion Without' the expander means the rings when finished are found to v'ai'y'jin size often as much as .010" or even more The per: c'enta'ge'of rejection'on accoiin 'of s'izeis negli giblewitli this simple eiipdifi The e is? I10 difficulty 'thre'adiri'gi'the ringsbverithe blade inasmuch as. it extends into triefierea ene' 22 of "thesiziiig rin'g'- and theses iiithrifigfifig sateen-4 there o" r sm'pi width at the point wiiereni e ringers ean-mere the blade. The ga es ere, er

fijjfg; Kept in line With the made" 2'! 53? the rib I1.

The spring blade 28 as clearly appears iii Fig. 7, "is" the reverse or the ihwardly'projb mg type it is u'sliaped and has the arms extending tenneny radially inwards relative to the 151's on riffg R, so that the two iid. ortions Have some engagement in th ring ga and serve to eg safiet e r n to the full inside diameter or the sled/e21. This externally projecting type periiiits oei etmg on'tne inner diameter with the 661 crime 25 without ans inter erence wan 'd'e; A i i' insert 53 or soft detail has one side e iiiiddjle or' C-b'n'd portion or the sews; bi a es'uitabiy fastene triereto, as by Brazing; in:- (If fastened so that the torsional reaction due to mag Oh the outer and inner peri heries is as}- su med' the fr'elihfiioiiabl and i ie'ldabie ies 6f tease blades, as, for examp e, the left re ii Fig, 6 and the right leg in Fig. 7, there n to t v advantage of the resilience of the spring bladed absorbing the: shocks and sotliat there will-be less danger of the blades being broken or breakir'ig free froth their supports.

It be etidfit that although I halidd scribed a machine in which both turning and Her ing are done} the same principle of operation n' ightb'e applied in a machine for 01113 turning or Q j-ly g} For example, by merely eliminating the in head 4|, Shaft 39; and bearing hill; I 5

provided for said shaft, the" fiiachiii is" still adapted for the rough turning and finish turning if g t i s beiiei red theioregoing description eon-vets a good understanding of the objects" and seven: tages of my invention. The appended clai'rhs have been drawn. to cover all legitimate media cations and adaptations.

1. In the manufacture of piston rings, or the like, aplurality of coa'ir'ially aligned supports, eac support having a bore therein adapted slidably to receive a plurality of piston rings in stacked relation face to face in the bore, whereby each'jring is" held properly positioned norrhal to axis of operation by tight contact of its 015'- poised fades with neighboring rings in the stack andflis held against displacement radially by cfontaot'with the bore, said supports having adj'o'inihg ends's'p'aced less than the width of a ring and enough topermitmachining the peripheries of the rings in the bores, means for moving the stac axiallyat a feed rate through the bores p'ast'a; plurality of tool stations at the a'fores'aid spaces betweensupports, and tools at said etatio'ns" for machining theouter periphe'ries'of-sai'd rmgs m the movement of the stack;

- 2; mthe manufacture of piston rings, or the tied at 54, The blades 21, 2 and 511 I 7 at a feed rate through the bores past a tool station at the aforesaid space between the supports, and tool means at the tool stationfor machining one of the peripheries of the rings in the movev ment of the stack.

3. In the manufacture of piston rings, or the like, a pair of coaxially aligned supports, each support having a bore therein adapted slidably to receive a plurality of piston rings in stacked relation face to face in the bore, whereby each ring is held properly positioned normal to an axis of operation by tight contact of its opposed faces with neighboring rings inthe stack, andis held against displacement radially by contact with the bore, said supports having adjoining ends spaced less than the width of aring and enough to permit machining the peripheries of the rings in the bores, means for moving the stackaxially at a feed rate through the bores pasta toolstation at the aforesaid space between the supports and tool means at the tool station for machining the outer peripheries of the rings in the movement of the stack. 7 a

4. In the manufacture of split piston rings, or the like, a plurality of coaxially aligned supports,

such expose ring in contact with, the, bore, and,

whilepmovin he stack-axially in the borepast said stationajt affeed rate, machiningthe respective rings..i circumferentially on their outer peripheries; at'said station. V a

, Ti. Thefmethod of making piston. rings which consistsfin placing a series of split rings as a cylindricalstack. in a boreso that each of said rings held positioned normal to an axis of operation bytight contact of its opposed faces withgneighboringrings in the stackand is held against ,displacement" radially by contact with the bcreijexposing at a station. in an intermediateportio'n of the travel of the rings in the bores. orti n .ofth outer. perip ry-of Jrins in th bore'circiimferentially at saidstation wfil ll'liachining,, suppor ting theremaining portion .of

each support having a bore therein adapted. slidably to receive a plurality of piston rings in stacked relation face to facein the bore, whereby each ring is heldproperly positioned normal to an axis of operation by tight contact of its opposed faces with neighboring rings in the. stack and is held against displacement radially by contact with the bore, said supports; having adjoining ends spaced less than the width o faring and enough to permit machining theperipheries L of the rings in the bores, means for moving; the

stack axially at a feed rate through the bores past at least one tool station atthe aforesaid space between supports, guide means in the bores slidably engaged in the gaps of the rings to hold a the rings against turning whentheyfare being machined, and tools at said station for machining the outer peripheries .of .said 'ings in the movement of the stack.

5. In a machine .of the class described... the combination of a hollow cylindrical stationary support adapted for slidably supporting a stack of piston rings. or the like in the bore .thereof,.a sizing ring in the outgoing endportion of the bore having a taper in the borethereof on the incoming side in which rings. areclosedgradually to a predetermined outside diameter whilefbeing moved through the sizingring, .means'for moving the stack of rings at a feed rateaxialiy through said support and sizing ring,. rotary .turning means sup-ported in concentric relation .torsaid sizing ring and arranged to operateon the ex,- posed portion of the periphery of- .the rings. in their passage out of the sizing: ring, andmeans for guiding the rings by the machined portion 01' their outer peripheries to help keep the-same centered relative to the sizing ring While they are being machined on their outer peripheries.

6. The method of'making piston rings which consists in placing a series or splitringspaaa cylindrical stack in a bore 'so thateach-of said rings is held positioned normal to anaxis of operation by tight contact of its opposed. faces with neighboring rings in the. stackand is held against displacement radially by. contact with such expcsedi ring in contact with the b rean while moving the. stack axially in the bore past said stationfat a feed rate, contracting the rings in,succession. .m a predetermined outside diameter at said'station and, while still so contracted, machining. the respective rings circumferentially ongtheir quterperipheries at said station. 8 The method of making piston rings which consists in placing a series=ofr split rings as, a cylindricalstack ina bore so that each ofsaid rings isflheldgpositioned normal to an axis pf peratio ..hy...tieht.. o taqtoi opp sed faces with'nei'ghboring rings injhe stackandis. held against displacement radially by contact with the bore, exposing enough ofthe outer peripheries of the rings in the borecircumferentially ata stationfor machining, and, while moving the stack axially in the. bore past said station at a feed rate, expandingfthe rings in succession to a pree m nedbuts de diame at Said t n. and. while still so expanded, machining the same cincumferentially gri their outer peripheries.

9. .irhe' metho f. m piston s. Wh consists in'p cine a series of split rings asa cylindrical stack "in a bore so that each. of said rings is held positioned normal to an axis of operation by'tight contact of its opposed faces with neighboring rings in the stack and is held against displacementradially by contact with the bore, and, while moving the stack axially in expanded, machining the same on their inner peripheries,

;l0.,.In' a machine for machining resilient split work. s as e hi tamine en t mbin tion of a m'ain externalchuck, and an auxiliary externalchuck aligned with the main .chuckrto recei elwo'r adva e th eto from. t ma n chucknthe main chuck being internally reap wardly ,taper'edflto contract and grip resilient worksaidmain, chuck and a throat being pro,- vided withan aligning rib engaging thespli't of the work, rneians for feeding a plurality of pieces of workdisposed in side'by side relation into-said mainchuck and, acutter acting onthe work. as it is projected from themain' chuck and delivered into said auxiliary chuck, the distance between saidmain and auxiliary chucks being such that a machined'portion of the work is received within the auxiliary. chuck priorto-thecomplete dis.- chargeof workvfrom ,themain chuck said aux; iliary chuck having .an internal aligning .rib aligned with the aligning ribof said mainchuck,

. ll. a machine for, machining resilient split worksuch piston'ring elements, the combine;- pn' ja attendee- 9 s ensw a external chuck aligned with the main chuck to receive work advanced thereto from the main chuck, the main chuck having a cylindrical work holding portion at its discharge end and an elongated throat having a rearwardly tapered portion for contracting work advanced through the throat, means for feeding a plurality of pieces of work disposed in side by side relation into said throat whereby they are contracted and frictionally supported as they are advanced into the mainv chuck, and a cutter acting on the work as it is projected from the main chuck and delivered into said auxiliary chuck, the auxiliary chuck being internally cylindrical at its front end and of an internal diameter corresponding to the diameter of the machined work, the distance between said main and auxiliary chucks being such that a machinedportion of the work is received within the auxiliary chuck prior to the complete discharge of work from the main chuck.

12. The method of manufacturing piston rings comprising the steps of advancing a plurality of split resilient piston ring elements in side by side relation into a tapered chuck first acting to compress and frictionally hold the same, and delivering the ring elements from such first chuck to a second chuck aligned therewit, and externally machining the ring elements as they are successively discharged from the first chuck to the second chuck, the distance between the chucks L being such that the work is received by the second chuck prior to its complete discharge from the first chuck.

13. In a machine of the class described, the combination of an external chuck adapted to contract and grip work advanced therethrough and having a cylindrical work holding portionat its discharge end, said chuck having an elongated throat provided with a rearwardly tapered portion for contracting work advanced therethrough, said chuck and its throat being provided with an aligning rib toengage the split of work such as split piston ring elements, means for advancing a plurality of pieces of Work disposed in side by side relation into said throat whereby they are contracted and frictionally supported as they are advanced into the chuck, and a cutter disposed at the rear of the chuck to act on the outer circumference of a ring element at the rear of the chuck, said aligning rib engaging the split of the ring element acted upon by the cutter and spaced from said cutter to permit the cutter to cut the ring element without engaging the aligning rib.

14. A machine for machining split piston rings comprising an internally tapered main chuck adapted to contract work advanced therein, an auxiliary chuck adapted to receive work discharged from said main chuck, means for advancing a plurality of pieces of work in side by side relation in said main chuck, and a cutter operatively associated with said main and auxiliary chucks to act on the work as it is trans ferred from said main to said auxiliary chuck.

15. The method of manufacturing piston rings comprising the steps of advancing a plurality of split contractible piston ring elements in side by side relation into a tapered first chuck acting to compress and externally grip the elements, delivering the ring elements from such first chuck to a second chuck aligned therewith, and externally machining the ring elements as they are projected from the first chuck, the distance between the chucks being such that the work is received by the second chuck prior to its complete discharge from the first chuck.

ALBERT H. BATES.

REFERENCES CITED The following references are of record in the file of this patent:

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